It's possible you're conflating asocial and antisocial behavior.
Humans are social creatures and we communicate in more than just words. How you respond to people, or in this case don't respond to people, says a lot to them. What the other person interprets may or may not be true. Frankly, humans are prone to storytelling so they have a tendency to presume the worst. If you aren't reinforcing otherwise with your words and your behavior, then they will naturally become upset.
I'm really really glad to hear that you have people in your life that seem to care about you, ask about how you are, and provide various things for you. However, even though you may not feel like it for whatever reasons, refraining from reciprocating that behavior will starve out those relationships.
Human relationships are always quid pro quo. If you are receiving, then you will be giving something back. It doesn't have to be one-to-one and not usually immediate.
If you want relationships of any kind to be healthy, then reciprocating when people invest into you is important. Again, it doesn't necessarily have to be in the same way or amount, but there does have to be a response. Without that, the relationship becomes unhealthy or eventually over.
On a side note, I'm really proud to see you being forthright and honest with your mental health. I know it's more commonly spoken about these days, but it can still be hard. I hope that you're getting help as you navigate through it. You might find that some of the internal healing work you do will also positively affect the very relationships you are talking about in this post.
For the first question, you might find answers more helpful if you ask the aforementioned people that you're actually interacting with.
And regarding the second question, it's probably related to the first. Young people who grew up texting and using social media have adopted abbreviated writing styles. Older people using the same technologies tend to retain more proper forms. Of course, people aren't monoliths. There's plenty of young people writing in complete sentences and plenty of older people utilizing short form words.
I tell her to be nice and to love her stuffies, but even the ones that are designed to be super tough somehow always manage to offend her and get their guts pulled out.
Every time I see this statement, my first reaction is to feel solidarity, "yeah!" Then I think about all those emails I don't read and never respond to... 😅
"Being yourself" does not preclude personal development. Personal growth and learning skills, even something like flirting, is part of becoming a more well-rounded version of yourself.
Thing is, flirting isn't something you need to master or even be great at. As a matter of fact, being "terrible" at flirting can be just as effective.
The goal of flirting is to engage in social interaction that expresses interest and attraction.
I think you're putting too much pressure on yourself. You probably shouldn't even call it flirting. Put that notion aside. Focus on intentionally communicating your interest.
If you're interested in a person, then find ways to express that. It can be light-hearted and flirtatious, but being terrible at flirting works too. So do it terribly. You'll eventually figure out what doesn't help communicate your intent. Flirting is a gentle and indirect way of expressing that intent. Many people are more direct and it can work for them too. Being more direct may be better for you. 🤷🏽♂️
Regardless of what you do, be respectful. Be playful if you want. But most importantly, communicate your intent and desire.
Watch some romance movies... even... Hallmark movies. Emulate no more than 20% of what you see and that will be sufficient. Too much more than that will cause an aneurysm. And realistically, normal human interactions are not nearly as concentrated as those movies. It'll give you the basics.
In other words, you show romantic interest by showing romantic interest.
💜